PAR lamps are typically comprised of a light source such as a tungsten halogen capsule or a high intensity discharge (HID) arc tube mounted within a glass body with a parabolic reflector therein. The glass body can be pressed borosilicate glass. A lens usually covers the front or light-emitting end of the body and can contain optical elements to provide a desired beam shape (for example, a spot or flood beam). General service PAR lamps usually have a neck region between the parabolic reflector and the base, and the base generally comprises a threaded fitting for connecting the lamp to a power source via a socket. The usual power source is 100 to 240 volts. The neck provides the mechanical support between the reflector optical portion and the base electrical portion. The neck additionally provides room for the capsule press seal, the lead-ins, capsule mounting components, and wiring and separates the light source (i.e., the filament or arc discharge) from the base to reduce the base temperature.
Much of the light that enters the neck opening of PAR lamps is lost due to multiple reflection and absorption by the mount and capsule components and does not contribute to the beam. It is known that the neck opening cross-sectional area should be as small as possible to maximize beam intensity and lamp efficiency (determined by dividing lamp lumens by source lumens). The marketplace demands compact lamps with small diameter aperture such as PAR 16 and PAR 20 size lamps; however, as lamp diameter and reflector focal length decrease, the light loss in the neck area becomes substantial. Lumen output and center beam candle power (CBCP) fall off rapidly as PAR lamp size decreases and it is very difficult to design a PAR 16 spot lamp with acceptable performance. At this point in time, PAR 16 lamps are available only in a flood beam angle where the light center can be positioned ahead of the focus and away from the neck opening without an unacceptable loss in center beam intensity.